The present invention relates to a retromodulator in the form of a triple mirror.
Retromodulators are needed, for example, for the transmission of data, for which on the transmitter side only a limited reserve of energy is available which does not permit emission of high power signals. This is the case, for example, with satellites, military missiles, monitoring stations, etc. By using a retromodulator, one can proceed as follows: The retromodulator receives a light beam originating from the calling station, modulates it with the data to be transmitted, and reflects the light beam back to the calling station. (By light is understood here a spectral range extending for example, from 0.3 to 20 .mu.m).
A retromodulator in the form of a triple mirror is known, for example, from DE-PS No. 32 30 159. In this retromodulator, the triple mirror consists of two fixed continuous mirror surfaces and of a mirror surface which is composed of a pattern of mirror surface elements. On the back of some of the mirror surface elements piezoelements are applied. Without a voltage applied to the piezoelements, all mirror surface elements are coplanar; by an applied voltage, the part of the mirror surface elements on which piezoelements are applied is displaced in accordance with the voltage, so that there results a phase modulation of the incident radiation retroreflected by the retromodulator.
While this known retromodulator permits modulation of the reflected light at high frequency, its construction is complicated due to the many separate mirror elements with the respective piezoelements, so that the known retromodulator is expensive to manufacture.
Moreover, high voltages in the kV range are necessary, to produce piezo deflections in the order of micrometers.
From U.S. Pat. No. 4,216,440, a prism consisting of piezoelectric material is further known, on whose sides finger-like electrodes are vapor deposited. While the manufacture of this prism is comparatively inexpensive, being a one-piece prism of piezo material, no great modulation magnitudes and high modulation frequencies are possible due to strong internal forces.